TECHNICAL REPORT
Inexpensive Electronic Flame
Flicker Effects for the Theatre
Traditionally, lighting technicians
have attempted to simulate the effect of
live flame on stage primarily by turning
lamps on and off at irregular intervals.
One popular method, for instance,
consists of connecting a fluorescent
lamp starter in series with a low to medium wattage lamp. However, in other
situations this and similar techniques
may prove impractical. The fluorescent
starter-based effect, for instance, cannot be dimmed appreciably. Furthermore, such switch- based effects suffer
from an intrinsic esthetic limitation in
that any individual lamp is only capable
of two levels of brightness and this is
usually too blatant for exposed candle
and chandelier flame lamps. The electronic flicker effects to be described
here largely overcome these difficulties.
Fundamentally these electronic
flame flicker effects consist of a number of square wave generators operated
asynchronously, whose summed output
appears as a randomly rising and falling
current or voltage which is used to produce a randomly rising and falling light
output. Two forms of the device have
been constructed. The first is powered
from a battery source and is suitable for
hand carried effects such as lanterns.
The second version is designed to be
used downstream of a standard theatre
thyristor (SCR or TRIAC) dimmer.
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Figure 1. Schematic DIAGRAM: Flicker Effect-Battery Version.
Battery Powered Version
Both versions use two type 556 integrated circuits each of which consists of
two complete clocks in a single 14 pin
DIP package. In the case of the battery
powered circuit all the clocks are operated in their astable mode which is
to say that the output of each clock
switches continually from low to high
and back at a rare determined by external timing components. Referring to
lClA in Fig.!., for example, the fre22
Figure 2. Battery operated flicker effect circuit 1Il0dule. The type 1891 lalllp we
made "j/allle shape" by slightly heating a length of clear flexible plastic tubill
and then drawing it out to a point.
Theatre Design & Technology I USITT ISpring 1985

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